Sjtaylor

I知 learning about bicycle brakes. I just did a frame up rebuild of a Trek 720 and decided to upgrade the brakes for some from a 2013 520. I took the brakes and the drop bars. That gave me a cleaner cockpit with the cable housings under the tape rather than the Golden Arches look. The newer brakes had a longer moment arm and look to have better stopping power.

I ran into a fit problem and had to leave the old cantilever brake in the front with the newer one on the rear. I was aware of the different pivot distance between the old and new brake levers but I went ahead and installed that setup with the newer and more comfortable brake levers. My mistake was that I finished with a real nice bar tape wrap on the untried brake setup.

The difference between the braking power of the two brakes with the mismatched setup was unbearable. I thought I might notice just a small difference. I have to redo the setup and ruin that awesome bar tape job. Turns out I have a set of Tektro brake levers with the same pull as the originals. The fix is to keep the original brakes and change out the levers. That値l keep me busy for a couple hours.

I値l add that the 720 ride is way nice. On that test ride with those Schwalbe Marathon Plus 35c tires at about 40psi I was very comfortable.

fietsbob

The mechanics of Leverage comes in to this https://sciencing.com/calculate-mech...rage-2828.html

a lever is work/(brake pad, cable being pulled , fulcrum/ pivot ... & effort, where the force is applied.

those distances are a ratio.

https://en.wikipedia.org/wiki/Lever
higher MA moves less distance but its easier to move a high MA demand needs a lot of motion but the applied force is higher..

Sjtaylor

Thanks for the links. I’ll have a look.

Im a retired mechanical engineer and I passed my Statics and Dynamics classes. Too bad I didn’t do a better job applying that stuff.

Trial and error is how this went but I think I finally have it right.

Thanks again.

madpogue 

Rework is a good teacher.

Another good reason to defer handlebar wrapping on a build/mod is that you can't be sure, before riding it, of the best position of the levers on the bar.

BTW, you are hereby required to post pics of the final product, and/or any work in progress, to the "Show your Trek" thread over in C&V.

dedhed

https://problemsolversbike.com/produ..._agents_-_6416

Sjtaylor

Yeah, I’ll know better this next time. I did post what I thought was the finish build in the Show Your Trek Thread. I’ll post there again when I’m loaded up for the practice tour I’m planning. It’ll be a fifty mile day with a camp in Mom’s back yard.